Short Papers – IV South American Symposium on Isotope Geology

Rb-Sr AND Sm-Nd ISOTOPE GEOCHEMISTRY OF GRANITOIDS FROM ESPERANÇA GRANITIC COMPLEX, PARAÍBA STATE, BORBOREMA PROVINCE, NORTHEAST

Sampaio, M.A.1; Guimarães, I.P.2; Almeida, C.N.3 and Carmona, L.C.M.4

1. CPRM-RE e PG-UFPE. [email protected] 2. DGEO-UFPE. [email protected] 3 . DCR - CNPq - UFPB 4. PG-UFPE. [email protected]

Keywords: Granitoids, Neoproterozoic, Borborema Province, Brasiliano Orogeny

INTRODUCTION (including the Conceição type and some Itaporanga type The Neoproterozoic evolution of Borborema granitoids), which are examples the Tabira, and Province, Northeast Brazil, was characterized by an Timbaúba Complexes; high-K metaluminous calc- intense granitic magmatism, associated with a network of alkaline granitoids (Itaporanga type granitoids), including continental-scale transcurrent ductile shear zone the Fazenda Nova, Campina Grande and Esperança (Vauchez et al., 1995). Van Schmus et al. (1995, 1997) Complexes; syenites, quartz-syenites and syenogranites using U-Pb and Sm-Nd data, subdivided the Borborema of shoshonitic affinities, including Bom Jardim, Toritama Province in three tectonic domains: Northern, Central and and Pajeú Complexes; monzogranites, syenogranites and Southern, which have shown contrasting isotopic syenites, including the Solidão, the east part of Teixeira, characteristics The Central Tectonic Domain (CTD), Queimadas, Triunfo and Serra Branca Complexes; and region located betwen the continental shear zones Patos biotite syenogranites coarse to medium grained, and , had affected by at least three equigranular to slightly porphiritic (Prata Complex, thermotectonic events: Paleoproterozoic event Pereiro, Serra do Velho Zuza, Serra da Engabelada and (Transamazonian Orogeny, 2.2 to 1.8 G. a), Serrote Santo Antônio plutons). Mesoproterozoic event (Cariris Velhos Orogeny, 1.0 to 0.9 G.a.) and Neoproterozoic event (Brasiliano Orogeny, GEOLOGIC SETTING, GEOCHEMICAL AND 0.85 to 0.58 G. a), this last event was responsible for the MINERAL CHEMISTRY CHARACTERIZATION intense magmatism which characterized Borborema The Esperança Complex comprises late tectonic Province. Neoproterozoic intrusions, occupying an area of 580 km2 Santos (1996, 1999) subdivided the Borborema intruded in ortogneisses of Mesoproterozoic ages of the Province in tectono-stratigraphic terrains, with distinctive Alto Pajeú Terrain (APT), Central Tectonic Domain stratigraphic, structural and petrologic features. The (CTD) of Borborema Province. The emplacement of the Central Tectonic Domain (CTD) was separated in five Esperança Complex was controlled by transcurrent- parts: West Gneissic Terrain (WGT), Piancó-Alto Brígida extensional shear zones: Remígio-Pocinhos (Patos Terrain (PABT), Alto Pajeú Terrain (APT), Alto Moxotó Lineament segment) in north and São Sebastião de Lagoa Terrain (AMT), Rio Capibaribe Terrain (RCT). In the de Roça in the south. Alto Pajeú Terrain (APT), the magmatism was related at Petrographic data suggest that the Esperança Complex least to two orogenies (Cariris Velhos and Brasiliano comprises at least three intrusions, denominated north, events). The first event is characterized by low-angle south and west intrusions (Fig. 1). structures, associated with low angle kinematics, The north intrusion comprises porphyritic to wherever the last event is characterized for shearing equigranulate fine grained biotite amphibole syeno and structures, associated to an transcurrent kinematics. monzogranites; the south intrusion comprises coarse Almeida et al. (1967) recognized four types of grained, porphyritic biotite amphibole syeno and granitoids: Conceição type (granodiorites and tonalites, monzogranites. The west intrusion comprises coarse- medium to fine grained), Itaporanga type (granodiorites grained biotite amphibole monzogranites to quartz- with large phenocrystals of K-feldspar), Itapetim type monzonites. Biotite clots and syn-plutonic dykes of (biotite fine grained granites, associated to Itaporanga granodioritic to tonalitic composition occur in all type) and Catingueira type (peralkaline granites, syenites intrusions. Dykes of pegmatites and late leucocratic and quartz-syenites. Sial (1986) identified four granitoids alkali-feldspar granite are frequently recorded cutting the types in the Piancó-Alto Brígida Terrain: calcalkalic north intrusion. (Conceição type), potassic-calcalkalic (Itaporanga type), Several textural features, mafic clots, sin-plutonic peralkalic (Catingueira type) and trondhjemitic affinities dykes of granodioritic to tonalitic composition, and ( type). rapakivi and anti-rapakivi texture, suggest coeval Taking in consideration the crystallization age and relationships between distinct granitic magmas, possibly geochemical characteristics, using U-Pb zircon and Sm- implying processes of magma mixing and commingling. Nd data, Guimarães et al. (1999) divided the CTD granitoids into five groups: calc-alkaline granitoids

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N U-Pb ZIRCON GEOCHRONOLOGICAL DATA U-Pb zircon data were obtained from three multicrystal magnetic fractions from the porphyritic granites from the south intrusion (ESP-01), at the Isotope Geochemistry Laboratory, University of Kansas. The analyzed zircon population comprises euhedral internally clear pink zircon grains without any inclusions. The zircon grains were abraded for 2h and then washed with HNO3. The upper Concordia intercept defines an age of 581 + 7 Ma (MSWD = 1.2) when forced to zero (Fig. 2).

Figure 1. Geological sketching of Esperança Granitic Complex, PB. Modified from: Geological Map of Paraíba State, 2001, CPRM. Escale: 1/250.000.

The granitoids of the Esperança Complex are metaluminous to slightly peraluminous, and high-K calc- alkaline. REE patterns normalized to chondrite values, display two distinct patterns: the pattern of the North Intrusion have (Ce/Yb)N ratios ranging from 16.6 to 24.4 and lack of the significant Eu anomalies. The granitoids of the south intrusion have REE pattern less fractionated, with (Ce/Yb)N ratios ranging from 8.4 to 16.6 and strong Eu negative anomalies, similar to those patterns recorded in Figure 2. Concordia diagram for granitoids of Esperança A-type granites. Spiderdiagrams normalized to the Granitic Complex, PB. primitive mantle are characterized by troughs at Nb, Sr and Ti. Rb-Sr AND Sm-Nd ISOTOPIC DATA Compositions of feldspars, biotites and amphiboles Rb-Sr and Sm-Nd isotopic data of granitoids from the from the Esperança Complex granitoids also divided the north and south intrusions of the Esperança Complex, complex in three distinct intrusions: the plagioclase of the were obtained at the Isotope Geochemistry Laboratory, north intrusion are slightly Ca-richer (oligoclase- University of Kansas. No isotopic data are available for andesine) compared to the plagioclase of the South and the west intrusion. The results are showed in Tables 1 and East intrusion (oligoclase composition). Biotites from the 2. Esperança Complex divided their granitoids into three The granitoids of the Esperança Complex show εSr distinct groups: biotites from south intrusion show Fe# (580Ma) ranging from 8.2 to 62.3 and exhibited initial rates [100Fe/ (Fe+Mg)] values ranging from 64 to 66, Sr87/Sr86 always less to 0.708, suggesting represent I-type FeO/MgO ratios ranging from 3.14 to 3.39 and AlIV granites (Chappell & White, 1974). values ranging from 2.3 to 2.4; biotites from the north Sm-Nd data show distinct isotopic signatures, to the intrusion have Fe# ranging 36 to 53, FeO/MgO ratios north and south intrusions granitoids. Both intrusions IV ranging 1.6 to 2.0 and Al values ranging 2.2 to 2.3. exhibited εNd initials values strongly negative, suggesting Biotites from the west intrusion are Fe-enriched, shown crustal contribution in the source. Fe# values ranging 68 to 73, FeO/MgO ratios ranging 3.8 The granitoids of the north intrusion have εNd(0) values to 4.7 and AlIV values ranging 2.46 to 2.53. In the ranging –16.53 to –15.08, and TDM model ages ranging discriminant diagrams to magmatic suites for biotite from 1.82 to 2.1 Ga, suggesting a Paleoproterozoic mineral chemistry (Abdel-Rahman, 1994), the biotites source. The South Intrusion granitoids show ε values from granitoids of the north and south intrusions plotted Nd (t) ranging from –7.19 to –6.02 and T model ages ranging within the calc-alkaline field, while the biotites from the DM west intrusion plotted within the peraluminous field. from 1.50 to 1.57 Ga, suggesting mixture of Amphiboles from the all intrusions of Esperança Paleoproterozoic crust with juvenile Mesoproterozoic Granitic Complex are calcic (Leake, 1997), with (Cariris Velhos) or Neoproterozoic material (Brasiliano). The Esperança Complex granitoids of the compositions ranging from Fe-edenite to Fe-pargasite. ε ε Fe# values of the amphiboles analyzed from the northintrusion, plotted in the Sr initial vs Nd initial granitoids of the Esperança Complex define three distinct diagram (Harmon et al., 1984), show isotopic fields: 59 to 61 (north intrusion); 67 to 75 (south composition similar to those recorded in the lower crust intrusion) and 70 to 72 (west intrusion), reflecting (Fig. 3). The sample analysed from the south intrusion plotted within the I-type granitoid field. crystallization under different fO2 conditions.

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Table 1. Isotopic analysis obtained for Rb-Sr Method for the granitoids of Esperança Granitic Complex (PB State) (N) = North Intrusion; (S) = South Intrusion.

Rb Sr Sr87/Sr86i ε Samples Rb87/Sr86 Sr87/Sr86hoje Sr i (ppm) (ppm) (580Ma) (580Ma) ESP-03A (N) 148.0 1194.0 0.35698 0.70896 0.705997 30.888

ESP-08A (N) 125.0 989.0 0.36400 0.70938 0.706359 36.031

ESP-08B (N) 230.0 1010.0 0.65584 0.70869 0.703247 8.184

ESP-12 (N) 85.0 838.0 0.29212 0.71063 0.708206 62.274

PX-01 (S) 164.2 283.4 1. 66865 0.72092 0.707070 46.134

Table 2. Isotopic analysis obtained for Sm-Nd Method for the granitoids of Esperança Granitic Complex (PB State). (N) = North Intrusion; (S) = South Intrusion.

147 143 144 143 εNd(t) Sm Nd Sm / Nd /Nd Nd / ε TDM 144 144 Nd ( 0) (±580 Samples (ppm) (ppm) Nd today Nd i (Ma) Ma) ESP-03A (N) 5.9632 45.5536 0.07914 0.511401 0.511100 -24.13 -15.45 1822.4

ESP-08A (N) 4.3378 31.3306 0.08371 0.511437 0.511119 -23.42 -15.08 1843.0

ESP-12 (N) 4.6832 27.2022 0.10409 0.511440 0.511045 -23.37 -16.53 2155.4

ESP-01 (S) 6.9140 39.0374 0.10708 0.511930 0.511523 -13.82 -7.19 1568.2

PX-01 (S) 8.1498 45.2183 0.10897 0.511997 0.511583 -12.50 -6.02 1503.5

CONCLUSIONS Isotopic and geocronological data suggest that the Esperança Complex constitutes a post-collision multiple source intrusion, constituted by at least two distinct sources: 1) Paleoproterozoic lower crust (north intrusion) and 2) a mixture between Paleoproterozoic lower crust and juvenile Mesoproterozoic material (Cariris Velhos) or Neoproterozoic material (Brasiliano) (south intrusion). Mineral chemistry of the essential minerals and whole-rock geochemistry allowed identifying three distinct intrusions: south, north and west intrusions. In all of the three intrusions mixing processes between granite and granodiorite to quartz diorite magmas were recorded. The Fe# values of the mafic mineral phases point out that the west, north and south intrusions were crystallized under distinct degree of oxidation. The degree of oxidation in a magma is a function of dissolved water content, and the amount of Figure 3. Discriminant diagram for I-type and S-type granites, water in granitic magma may depend on the tectonic using initial ε vs initial ε values, to Esperança Granitic setting. Because all three intrusions have approximately Sr Nd Complex granitoids. CI = Lower Crust, CS: Upper Crust. the same crystallization age, the differences in redox state (Harmon et al., 1984) recorded in the Esperança Complex granitoids may reflect distinct source rocks.

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ACKNOWLEDGEMENTS guide to magma source region and magma-crust interaction. The authors wish to thank CNPq for support extended Phil. Trans. R. Soc. London, 310:709-742. through grant 141597/2000-3; to Prof. W. R. Van Leake, B.E. 1997. Nomenclature of amphiboles: Report of the Schmus - the Isotope Geochemistry Laboratory of the Subcommittee on Amphiboles of the International Mineralogical Association, Commission on New Minerals Kansas University, to Prof. Márcio Pimentel University and Mineral Names. Am.Mineral., 82:1019-1037. of Brasília, for making available the Rb-Sr data. Maria Santos, E.J. 1996. Ensaio preliminar sobre Terrenos e Tectônica Angélica Sampaio wishes to thank GEREMI-CPRM- Acrescionária na Província Borborema. In: SBG, Congresso , for financial support to cover her expenses during Brasileiro de Geologia, Resumos, 6: 47-50. the Symposium. Santos, E.J. 1998. Programa Levantamentos Geológicos Básicos do Brasil: Carta Geológica. Escala 1:250.000 REFERENCES (Folha SC.24-X-A- Belém do São Francisco). Brasília, Abdel-Rahman, A.F.M. 1994. Nature of biotites from alkaline, CPRM. calc-alkaline and peraluminous magmas. J. Petrol., 35(2): Sial, A N. 1986. Granite-types in Northeast Brazil: current 525-541. knowledge. Revista Brasileira de Geociências, 16 (1): 54- Almeida,F.F., Leonardos, O.H. & Valença, J. 1967. Review on 72. granitic rocks of Northeast South America. Recife, Vauchez, A., Neves, S.P., Caby, R., Corsini, M., Egydio Silva, IUGS/UNESCO, 41 p. M., Arthaud, M.H. & Amaro, V. 1995. The Borborema Chappell, B. W. & White, A.J.R. 1974. Two contrasting granite shear zone system. Journal of South America Earth types. Pacific Geology, 8: 173-174. Sciences, 8: 247-266. Guimarães, I. P., Silva Filho, A F., Almeida, C. N., Melo, E. B., Van Schmus, W.R., Brito Neves, B.B., Hackspacher, P.C. & Melo, S. C., Araújo, J.M.M. & Sales, A. 1999. Sm-Nd Babinski, M. 1995. U/Pb and Sm/Nd geochronological isotope geochemistry and U/Pb in zircon ages of the studies of the eastern Borborema Province, NE Brazil: Brasiliano granitoids from the Pajeú Paraíba Terrain, initial conclusions. Journal of South America Earth Borborema Province, Northeast Brazil. II South American Sciences, 8: 267-288. Symposium on Isotope Geology, Córdoba, Argentina. Van Schmus, W.R., Brito Neves, B.B., Hackspacher, P.C., ACTAS: 203-205 Babinski, M., Fetter, A. & Dantas, E.L. 1997. Application Harmon, R.S., Halliday, A.N., Clayburn, J.A.P. & Stephens, of U/Pb and Sm-Nd geochronology to understanding the W.E. 1984. Chemical and isotopic systematics of the geotectonic history of the Borborema Province, NE Brazil, Caledonian intrusion of Scotland and Northern England: a and its implications for the evolution of West Gondwana. South America Symposium on Isotope Geology, Campos do Jordão, São Paulo, Brazil. Extended Abstracts, p. 27-29.

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